1. Technical Field
The present invention relates to a vehicle active suspension system, and is particularly directed to a method and apparatus for controlling the active suspension system.
2. Background Art
Vehicle active suspension systems are well known in the art. Such suspension systems have as their goal the control of the relative motion between the sprung mass (the vehicle chassis) and the unsprung mass (the suspension arms, wheels, tires, etc.) of the vehicle. An active suspension system may comprise (i) an actuator connected between the vehicle chassis and a vehicle wheel, (ii) a plurality of remote sensors which provide sensor signals indicative of road and vehicle conditions encountered or to be encountered by the vehicle, and (iii) a control unit which processes the sensor signals and provides a number of control signals to control operation of the actuator. The control unit processes the sensor signals in accordance with a preprogrammed procedure stored in a memory associated with the control unit.
Such a known active suspension system is disclosed in U.S. Pat. No. 4,625,993. In U.S. Pat. No. 4,625,993, a control system generates modal force signals in response to signals from transducers sensing actuator load and actuator piston displacement at each corner of a vehicle. The modal force signals represent forces corresponding to the heave, pitch, roll and warp modes of vehicle movement. The control system generates control signals to control electrohydraulic servo control valves associated with the actuators at the corners of the vehicle to effect piston velocity and thereby desired vehicle attitude. The control signals can be modified by signals representing vehicle speed and lateral and longitudinal acceleration and under selective control of the driver of the vehicle.
Another known active suspension system is disclosed in U.S. Pat. No. 5,217,246. In U.S. Pat. No. 5,217,246, a microprocessor produces a plurality of modal forces which are based on measured heave forces and measured unsprung mass accelerations. The microprocessor then produces modified values of the modal forces based on measured actuator displacement values. The modified values of the modal forces may be further processed by the microprocessor to produce a demanded output of an actuator operatively connected between a vehicle body and a vehicle wheel. The actuator is operated to move the vehicle wheel up and down relative to the vehicle body as necessary to provide a desired "ride feel" and "handling characteristic" of the vehicle.